Many systems which require the non-volatile storage of digital data include a data storage device comprising a rotating magnetic coated disk and a transducer for reading and writing information stored on the magnetic material of the disk.
The transducers in such data storage devices are typically known as magnetic heads. After manufacturing, the magnetic heads may be evaluated on magnetic head and disk testers in order to measure their operational parameters and performance characteristics, which may include storage density, access speed to data locations, reliability, and data integrity. The mechanical part of such a tester is known as a spinstand. A spinstand generally includes a magnetic head support element and a rotatable magnetic disk pack support element, which is also referred to as a spindle. The magnetic head support element is slidably attached to the spinstand to facilitate linear movement of the magnetic heads relative to the disk and perpendicular to the axis of rotation (or equivalently, the spin axis) of the spindle. An example of a prior art spinstand is the Model S1701, manufactured by Guzik Technical Enterprises of San Jose, Calif., the assignee of the present invention.
To evaluate the magnetic heads, a test disk pack is installed on a spindle of a spinstand. A disk pack is a general term of art used to describe a set of one or more magnetic disks adapted for mounting as a unit on the spindle of a drive assembly. During testing, the disk pack may rotate at speeds exceeding 10000 rpm. Because the spindle of the spinstand rotates with such high speed, the spindle must be balanced carefully to avoid centrifugal forces which may cause vibrations of the spindle and disk pack mounted thereon and thus impair the accuracy of testing. Vibrations in the rotating elements can cause tracking errors of the magnetic heads over the disk track. Such tracking errors are particularly important in connection with high data density systems; the radial density of disk tracks in state-of-the-art data storage devices can be as high as 10000 tracks/inch. To minimize vibration, the continuum of centrifugal forces generated by the rotation of the disk pack are distributed uniformly about, and oriented perpendicular to, the axis of rotation. When the forces are so distributed, each centrifugal force vector generated by the disk pack is canceled by an equal force directed 180 degrees about the axis of rotation, so that no net force remains. An imbalance occurs when the centrifugal forces generated by the rotating disk pack are not uniformly distributed, and a net force directed radially outward from the axis of rotation remains because complete cancellation does not occur.
Since the disk pack, when installed on the spindle, will also rotate at high speeds, the disk pack must likewise be balanced to minimize vibration. In prior art systems, both the spindles and disk packs are balanced with general-purpose balancing machines, such as the BT-25 machine of Heins Balancing Systems, Inc.
Since the spindles are balanced independently of the disk packs, an imbalance may still exist when the disk pack is mounted to the spindle if the axis of rotation used to balance the spindle does not coincide with the axis of rotation used to balance the disk pack. Test disk packs must occasionally be removed from the spinstand and replaced as a result of damage or a revised test specification. Since each disk pack is unique, replacing a disk pack creates a potential imbalance and necessitates a new spindle/disk pack balancing procedure.
It is an object of this invention to provide a spinstand that is amenable to balancing of the spinstand spindle with a disk pack mounted on this spindle.
It is another object of this invention to provide a method for balancing a spinstand spindle with a disk pack mounted on this spindle.
It is a further object of this invention to provide a spinstand with a built-in automated system for imbalance measurements.
Yet another object of this invention is to realize automated means of balancing the spinstand spindle with a disk pack mounted on this spindle.